B7-H4 (VTCN1, B7x, B7S1) is a transmembrane protein belonging to the B7 family of costimulatory proteins and has been shown to inhibit T cell proliferation, cytokine secretion, and cytotoxic lymphocyte (CTL) induction. B7-H4 expressed on tumor cells or macrophages has been associated with poor prognosis and impaired T cell function in renal cell and ovarian cancers. Here we show B7-H4 is abundantly expressed in human breast cancer with triple negative breast cancer (TNBC) having the highest overall B7-H4 mRNA expression. We developed a specific and sensitive immunohistochemistry (IHC) assay for evaluation of B7-H4 protein and quantified B7-H4 expression in 156 breast tumor samples. Approximately 70% of the breast tumor samples had detectable B7-H4 expression whereas none of the normal or benign breast tissues stained positive for B7-H4. Multiplex IHC and flow cytometry studies showed that the majority of B7-H4 expression was restricted to the tumor epithelial cells, the CD45+ immune cells were negative for B7-H4 expression. Interestingly none of the TNBC samples that were positive for B7-H4 showed detectable expression of PD-L1 suggesting that B7-H4 and PD-L1 checkpoint proteins may act in a mutually exclusive manner.

To evaluate the role of B7-H4 on tumor immune evasion, we overexpressed murine or human B7-H4 on the mouse colon-26 (CT26) tumor cell line and injected these cells intravenously into Balb/c mice. By day 14 we observed significantly more tumors as well as larger percent tumor area in the lungs of mice given CT26 cells transduced with human or mouse B7-H4 as compared to vector control transduced cells. These data suggest B7-H4 expression in tumors can accelerate tumor growth in immune competent mice and that targeting B7-H4 may provide therapeutic benefit. Given the mutually exclusive expression patterns of B7-H4 and PD-L1 a B7-H4 targeting agent may provide particular benefit in those patients where current anti-PD-1/PD-L1 therapies are not effective.

Citation Format: Shaffer DR, Nagashima K, Cortez-Retamozo V, Feldman I, Smith J, Zafari M, Larson R, Mabry R, Novorantseva T, Briskin M, Sathyanaryananan S. Mutually exclusive expression pattern of the immune co-inhibitory molecules B7-H4 and PD-L1 in triple negative breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-07.